The frequency response of miniature receiver units is often limited. This applies in principle for all frequency responses, including both the high- and low-frequency response.
As an example, it is well-known that due to the limited membrane area as well as the limited stroke length the low-frequency response from miniature receiver units in open fittings is often rather weak. In order to improve and thereby increase this low-frequency response either the membrane area or the stroke length, or preferably both, must be increased.
Hearing aid receiver units are however often used in hearing aid instruments where the available space is very limited. An example of such a hearing aid instrument is the one being denoted receiver-in-canal (RIC) where the hearing aid receiver is positioned inside the ear canal of the user of the hearing aid instrument. Obviously, by positioning the hearing aid receiver inside the ear canal of the user puts high demands on the allowable outer dimensions of the receiver.
It may be seen as an object of embodiments of the present invention to provide a receiver unit having an enhanced frequency response.
It may be seen as a further object of embodiments of the present invention to provide a receiver unit having an enhanced low-frequency response without increasing the outer dimensions of the receiver unit significantly.
It may be seen as an even further object of embodiments of the present invention to provide an armature type receiver unit having an enhanced low-frequency response without increasing the outer dimensions of the receiver unit significantly.